


I Understand

by xXFontcest_SeptiplierXx



Category: Undertale (Video Game)
Genre: Alternate Universe - Underswap, Ecto-Penis (Undertale), Ecto-Vagina (Undertale), M/M, Masturbation, Mating Cycles/In Heat, Monster Heat, Sex, Skeleheat, Smut
Language: English
Status: Completed
Published: 2016-08-18
Updated: 2016-08-18
Packaged: 2018-08-09 12:41:04
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,029
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7802254
Author URL: https://archiveofourown.org/users/xXFontcest_SeptiplierXx/pseuds/xXFontcest_SeptiplierXx
Summary: <blockquote class="userstuff">
              <p>(Underswap) Papyrus is in heat and thinks Sans doesn't understand, but what happens when Sans understands more than he thought?</p>
            </blockquote>





	I Understand

**Author's Note:**

> So I used a few words that I'm not comfortable with using, but it fit with the story. Also, Sans is out of character a little (maybe a lot), but again it fit with the story. I apparently have an obession with writing the Underswap skelebros in heat as is apparent with this story, the one before it, and the ones I'm writing so I apologize for that. Hopefully the story is still good and I hope you enjoy! :)

Papyrus was in his room checking that his door was locked one last time. After he was sure the door was locked he went and sat on his bed. He sighed and relaxed a bit. He was in heat and heats were horrible.

Papyrus ran a hand under his hoodie and over his ribs. He then took off his hoodie and threw it on the ground. He ran his hand over his ribs again and felt as the heat went from his soul to his pelvis. He took off his pants before throwing them in the same direction as he hoodie. 

He ran his hand over his most sensitive ribs and moaned quietly. He then put a hand over his mouth to try and keep himself quiet. He moved his hand from his ribs to his pelvis where his magic was starting to form. Once his magic had formed he grabbed his member and started stroking it. He stiffled a moan as the wave of pleasure crashed over him.

He moved the hand that was on his mouth down to his soul. He gently held his soul in his hand and ran his thumb along the edge of it. He moaned softly at the sensation. All his actions froze when he heard a knock on his door.

"Papy, are you okay? You sounded like you were in pain."

Papyrus was in pain all right, not that he would tell Sans that. He kept the hand on his memeber moving, trying not to moan.

"I'm fine, bro."

"Are you sure?"

"Yeah."

There was silence from the other side of the door. Papyrus moved his hand faster, he was close.

"Papyrus, open the door."

"I said I'm fine."

He grit his teeth as he came. Just then he heard the lock to his door turn. Shit, he forgot about Sans's magic. He grabbed the cover at the end of his bed and covered up just in time for Sans to open the door.

"I didn't want to have to do that, but I'm worried and I want to know what's going on."

Papyrus sighed as he could feel the heat building up again. This wasn't going to turn out well was it?

"Okay, do you remember that time when we had the talk about heat?"

Sans nodded. 

"Do you remember what I said happens during heat?"

Another nod and then his eyes widened. A slight blue blush appeared on his cheeks.

"So you're in heat?"

It was Papyrus' s turn to blush. He then nodded. Papyrus really wished Sans would leave so he could get back to taking care of his heat.

Just then Sans came and sat next to him on the bed. He grabbed the cover and tried to pull it away from Papyrus. Payrus's grip tightened on the cover preventing Sans from taking it.

"Sans what are you doing?"

Sans looked up at him with his bright blue eyes.

"What does it look like? I want to help you."

"I don't think you understand what that means"

"I understand, Papy. I understood when we had that talk. I knew what heats were before that."

Sans ran a hand over Papyrus's ribs over the cover. A shiver ran up Papyrus's spine and his grip loosened. The cover fell so that it was only covering his bottom half.

"I understand that your bones are very sensitive right now, especially your ribs"

He said this as he ran his hands over each rib. He proceeded to wrap a hand around one of his ribs and stroke it. Papyrus moaned.

"I understand that you've gotten off at least once."

He moved the cover with his free hand. That same hand ran over Papyrus's pelvis, avoiding his member. 

"I understand that I'm teasing you by not touching your dick"

Papyrus moaned at that. It was hot hearing his "innocent" brother say such lewd words. Just then Sans grabbed his erection and began to stroke it causing Papyrus to let out a strangled moan.

"I also understand that to help you through this heat faster, I should form a pussy and let you fuck me."

Papyrus moaned loudly at those words. He was right and just hearing him saying it made him even harder.

"Please, Sans, I need it!" Papyrus panted out.

Sans pulled down his pants to show the entrance that he had formed. He laid back, pulling Papyrus on top of him. Papyrus lined the head up with Sans's entrance then looked up at Sans's face.

"It's okay, Papy. Go ahead."

Papyrus pushed in slowly then stopped when he was fully inside. He looked at Sans's face again to see him trying his best to adjust quickly. Then Sans gave him a nod.

Papyrus pulled out slowly then pushed back in just as slowly. He kept this pace for a bit before speeding up a little.

"Papy you can go faster."

Papyrus started going faster as he could feel the heat building and he knew he was close. 

"Sans I'm close."

"Let it happen."

Papyrus gave a few more thrusts before he fell over the edge with a loud moan. Sans came soon after, feeling Papyrus release inside him. Papyrus panted feeling the heat build again.

"Sans, I need one more round at least."

Sans pushed him back so he was lying on his back with Sans on top of him. Sans then lifted himself up and dropped back down causing both of them to moan. Papyrus thrusted up as Sans dropped down causing Sans to let out a loud moan. 

"Sans please, faster!"

Sans sped up pushing both of them to the edge faster. Papyrus felt the heat build up and knew he was close.

"Sans I'm gonna-"

"I know. Me too."

Sans slammed down sending both of them over the edge with loud moans. Papyrus pulled out and Sans collapsed next to him, both of them panting. Papyrus chuckled.

"When did you grow up and become so lewd?" 

"Oh shut up."

Sans then rolled over and laid his head on Papyrus's chest and snuggled into him. Papyrus wrapped and arm around him and smiled contently. Then they both fell asleep.


End file.
